System for the recognition of an optical signal and materials for use in such a system

ABSTRACT

A system and method for distinguishing a first light source from other light sources utilizes an image receiver that can selectively engage and disengage a filter. The filter can be configured to either block bands of light corresponding to the light being emitted by either the first source or the other sources. By sequentially engaging and disengaging the filter from the image receiver, the first light source may be distinguished from other light sources.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of co-pending U.S.provisional application Ser. No. 60/874,066 filed on Dec. 12, 2006. Thedisclosure of the co-pending provisional application is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a system for transmitting and receivinglight and more particularly to a system where an image receiver candistinguish between multiple light sources.

BACKGROUND OF THE INVENTION

Various kinds of lights are commonly used for assistance and guidance.For example, white lights on cars can be used to illuminate roads in lowlight or no light conditions, and colored lights on traffic signals canbe used to deliver information such as whether a driver should stop orproceed. Lights can also be used to identify locations such as in thecase of the lights used to illuminate a bridge as well as to identifythe presence of a moving object such as in the case of automobile breaklights. Numerous analogous uses of lights can also be found in a myriadof other industries and applications.

At times when there are multiple light sources it can sometimes bedifficult to decipher the significance of any one particular lightsource. For example, if the city street lights or lights used toilluminate a street sign are red, then it can be confusing for a driverto determine which lights serve as a signal to stop and which are merelyused to identify the location of a sign or a street. Additionally, aplurality of light sources might be able to identify a plurality oflocations or objects, but those sources cannot provide any informationregarding individual locations or objects within that plurality. Forexample, when driving at night, headlights and break lights can makeautomobiles visible, but they cannot give any additional informationabout individual automobiles such as whether the vehicle is a police caror whether the vehicle has a certain level of security clearance.

Based on the foregoing limitations of current lighting systems, itwould, therefore, be desirable to design a lighting system that candeliver more information than lighting systems currently known in theart.

BRIEF DESCRIPTION OF THE INVENTION

A system embodying aspects of the present invention can include a firstlight source having a first spectrum and an image receiver that candiscriminate between the first light source and other light sources. Thefirst light source might transmit light over a broadband spectrum andutilize one or more optical filters to selectively absorb or reflectback one or more wavelength bands, thereby altering the spectrum of thetransmitted light. Alternatively the first light source may have aunique spectrum from other light sources and not require furtherspectral modification via filters.

The transmitted light can be detected by an image receiver outfittedwith a second optical filter. The second optical filter can beselectively chosen to be in optical communication with the first lightsource. For example, the second filter might exhibit a reflection and/orabsorption spectrum that corresponds to the transmission spectrum of thefirst light source. When the second filter is engaged with the imagereceiver, the first light source can be blocked whereas other lightsources without a modified spectrum can be transmitted through thesecond optical filter and observed by the image receiver. When thesecond filter is not engaged, the first light source and the other lightsources may all be observed. Thus by alternatively engaging anddisengaging the second optical filter, the first light source may bedistinguished from the other observable light sources.

Another aspect of the present invention can include having the secondfilter exhibit a transmission spectrum that corresponds to thetransmission spectrum of the first light source. When the second filteris engaged, the first light source can be transmitted to the imagereceiver whereas other light sources without a modified spectrum can bereflected or absorbed. When the second filter is not engaged with theimage receiver, the first light source and the other light sources mayall be observed. Thus by alternatively engaging and disengaging thesecond optical filter, the first light source may be distinguished fromthe other observable light sources.

Another aspect of the present invention can include having one portionof the spectrum of the first light source provide illumination whileanother portion of the spectrum of the first light source may have aunique or altered spectrum allowing for it to be distinguished fromother light sources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example of a system embodying aspects of the presentinvention.

FIG. 2 is an example of a broadband light source and the filteredspectrum.

FIG. 3 shows the light incident upon a detector from the filter of FIG.1.

FIG. 4 is the UV-Visible Spectrum of an IR absorbing thin film accordingto an embodiment of the present invention.

FIG. 5 is the UV-Visible Spectrum of thin films made from Epolin 1125and Epolin 1175.

FIG. 6 is the UV-Visible Spectrum of thin films made from Epolin 4105and Epolin 4138.

FIG. 7 is the UV-Visible Spectrum of thin films made from some exemplaryUV absorbers.

FIG. 8 is the Visible-Near IR spectrum of the multilayer film made fromhot mirrors.

DETAILED DESCRIPTION OF THE INVENTION

A system embodying aspects of the present invention can include a firstlight source having a first spectrum and an image receiver that candiscriminate between the first light source and other light sources.

FIG. 1 schematically depicts an exemplary operation of a systemembodying aspects of the present invention. The system can include afirst light source 101 for producing light (shown by dotted lines 101L)over a first spectrum of wavelengths and an image receiver 103 capableof distinguishing the light 101L produced by the first source 101 fromlight 102L produced by other light sources 102 a-b. The first lightsource 101 might transmit light 101L over a broadband spectrum andutilize a first optical filter or series of filters (also referred to asa transmitting filter) (shown by element 105) to selectively absorb orreflect back one or more wavelength bands, thereby altering the spectrumof the transmitted light 101L. The image receiver 103 can manually,mechanically, or electronically engage a second optical filter 104 (alsoreferred to as a receiving filter). When the image receiver 103 engagesthe second optical filter 104, certain bands of light can be absorbed orreflected while other bands can pass through the filter 104 to the imagereceiver 103. When the second optical filter 104 is not engaged, theimage receiver 103 will receive all light being transmitted, includinglight from the first light source 101 as well as the other sources 102a-b, and the first light source 101 might be indistinguishable fromother light sources 102 a-b by the image receiver 103.

The second optical filter 104 can be configured to reflect or absorblight at one or more wavelength bands (stopbands) corresponding to thewavelength bands emitted by the first light source 101. In theseinstances, the other light sources 102 a-b can emit at wavelengths thatare removed from the spectrum of the first light source 101 by the firstoptical filter 105. For example, the first and second light sources 101and 102 might emit in the full visible spectrum (roughly 400 nm to 700nm). The first optical filter 105 might be configured to remove thewavelength band from 400 nm to 550 nm from the light 101L emitted by thefirst light source 101, only allowing light in the band from 550 nm to700 nm to be transmitted. Thus, if the second optical filter 104 isconfigured to reflect or absorb light of wavelengths ranging from 550 nmto 700 nm, then none of the light 101L emitted by the first light source101 will be transmitted to the image receiver 103, while the 400 nm to550 nm band of the other light sources 102 a-b will pass through thesecond optical filter 104 and be detected by the image receiver 103.Therefore, the image receiver 103 will be able to detect the other lightsources 102 a-b but not the first light source 101 when the secondoptical filter 104 is engaged. When the second optical filter 104 is notengaged, both the first light source 101 and the other light sources 102a-b will be detectable by the image receiver 103. Thus, by alternatelyengaging and disengaging the second optical filter 104, the first lightsource 101 and other light sources 102 a-b can be distinguished from oneanother.

In an alternative embodiment, rather than removing a portion of thevisible spectrum from the first light source 101, the first opticalfilter 105 might remove a portion of the non-visible spectrum. Thus, thefirst and other light sources 101 and 102 a-b might lookindistinguishable to the human eye but still be distinguishable by theimage receiver 103.

In the embodiment described above, the image receiver 103 candistinguish between the first light source 101 and other light sources102 a-b by alternatively filtering and not filtering all or a portion ofthe light spectrum emitted by the first light source 101. In analternative embodiment, the image receiver 103 can distinguish betweenthe first light source 101 and other light sources 102 a-b byalternatively filtering and not filtering all or a portion of the lightspectrum emitted by the other light sources 102 a-b. For example, theother light sources 102 a-b might emit in the portion of the visiblespectrum from 500 nm to 700 nm while the first source 101 emits over theentire visible spectrum (approximately 400 nm to 700 nm). Thus, if thesecond optical filter 104 is configured to reflect or absorb light ofwavelengths ranging from 500 nm to 700 nm, then none of the light 102Lemitted by the other light sources 102 a-b will be transmitted to theimage receiver 103, while the 400 nm to 500 nm band of the first lightsource 101 will pass through the second optical filter 104 and bedetected by the image receiver 103. Therefore, the image receiver 103will be able to detect the first light source 101 but not the otherlight sources 102 a-b when the second optical filter 104 is engaged.When the second optical filter 104 is not engaged both the first lightsource 101 and the other light sources 102 a-b will be detectable by theimage receiver 103. Thus, by alternately engaging and disengaging thesecond optical filter 104, the first light source 101 and other lightsources 102 a-b can be distinguished from one another.

Another aspect of the present invention can include having the firstlight source 101 emit in both the visible and infrared portions of thespectrum, as many white lights naturally do. The first light sources 101can provide illumination in the visible portion of the spectrum and canprovide information, such as identification information in the infraredportion of the spectrum. The first optical filter 105 can modify theinfrared portion of the spectrum of the light 101L emitted from thefirst light source 101, and the image receiver 103 can be configured todetect both the visible and infrared portion of the spectrum. Thus, whenthe optical filter 104 on the image receiver 103 is not engaged, a userof the system will see only the visible light being produced by alllight sources. However, when the optical filter 104 is engaged, the userof the image receiver 103 will be able to distinguish between the lightsources because some will be emitting infrared light and others willnot.

Another aspect of the present invention can include applying the firstfilter 105 to the first source of light 101 in such a way that theemitted infrared light carries digital information, such as anidentification number. For example, the portion of the infrared spectrumbetween 1000 nm to 9000 nm might be divided into 8 bits such that 1000nm to 2000 nm is the first bit, 2000 nm to 3000 nm is the second bit,and so on. Based on the configuration of the filter used, some rangeswill emit lights and other will not (i.e. some bits will be “on” andsome will be “off”). Emitting within the range corresponding to a bitmight de characterized as an “on” or “1” while not emitting within arange might correspond to an “off” or a “0.” For example, if it is knownthat the lights on ambulances do not emit light between 1000 nm to 2000nm, 3000 nm to 4000 nm, and 6000 nm to 7000 nm but emit in the otherportions of the infrared spectrum, then it might produce a digitalidentifier of 01011011. An image receiver 103 might include a series offilters configured to isolate the wavelength ranges corresponding toeach bit. For example, a filter corresponding to the first bit mightonly transmit light in the band from 1000 nm to 2000 nm, a filtercorresponding to the second bit might only transmit light in the bandfrom 2000 nm to 3000 nm, and so on. Therefore, a user of the imagereceiver 103 can confirm the digital identifier produced by theambulance by seeing whether each bit is a 0 or 1. Other types ofvehicles such as police cars and fire trucks might each have different,unique 8-bit identifiers.

It is contemplated that a system embodying aspects of the presentinvention is not limited in the types of applications in which it mightbe implemented. For example, an image receiver 103 might take the formof a camera system, night vision goggles, or other display devices suchas monitors or location instrumentation. Likewise, the first lightsource 101 might be implemented into devices such as automobiles orother transportation devices, personal lights attachable to the humanbody, identification lights such as those used to illuminate a road orrunway, or virtually any other type of light emitting system known inthe art.

Nonlimiting examples of light sources can include broadband lightsources such as incandescent lights, halogen lights, deuterium, xenon,or metal halide arc lamps or other light sources with a unique spectrumsuch a as fluorescent lights, sodium vapor lamps, light emitting diodes,white light LEDs employing Ce: YAG or other phosphors, RGB multichipLEDs, lasers etc. Nonlimiting examples of optical filters can includeinterference filters (bandpass, long, pass, short pass, hot and coldmirrors etc.), glass color filters, polymers or gels containing dyes orpigments. The filters may be affixed to a light source or an imagereceiver. The image receiver may be manually, mechanically, orelectrically engage or disengage a single filter or a plurality offilters.

Nonlimiting examples of image receivers 103 can include a cameraconnected to a display monitor, a pair of glasses, or any other commondetection device to which a filter might be attached. Additionally,infrared detection equipment including infrared cameras, night visiongoggles (NVGs), other night optical devices (NODs) sensitive to infrared(IR) wavelengths as well as visible wavelengths can be used as imagereceivers for detecting near IR wavelengths (approximately >750 nm) thatare otherwise undetectable by the unaided eye.

Nonlimiting examples of first optical filters 105 and second opticalfilters 104 can include interference filters comprising dielectric andor thin metal film stacks deposited on a glass or plastic substrates, ordyes, pigments or other absorbing materials dispersed within or on thesurface of polymer, glass, or gel films, plates, or other opticalsubstrates. The first optical filter 105 may be in the form of lenscaps,covers, mirrors (hot and cold mirrors), tunable optical filters, tunableLyot filters, liquid crystal tunable thin film filters, or other opticalsystem in which the first light derived from the first light source 101may be passed through. The second optical filter 104 may take the formof lenscaps, standard optical filters, or eyeglasses that may bemanually, mechanically, or electronically engaged with the imagereceivers 103.

Filters for the first light 101 source and the image receiver 103 can bemade from any combination of absorbing materials such as thin filmmolded parts incorporating absorbing dyes and pigments. The filter 105for the light source 101 might commonly be produced by incorporatingdifferent concentrations of absorbing dyes into extruded films and/orinjection molded parts. Alternatively, interference filters comprisingstacks dielectric and dielectric/metal films known in the art can beused. Filters 104 for the image receiver 103 can be produced byabsorbing materials or other techniques such as interference filters,etc. Many of these filters are sensitive to the angle of incidence ofthe incoming light so the spectral transmittance can vary with theincident angle of light. The light source filter and the detectionfilters need to be complementary in order to form an optical lock andkey. There are many examples of filters that could be used. Any filtersthat block one or multiple signals in the UV, visible or infraredspectrum can be employed. An exemplary interference filter might be whatis known as a hot mirror. This type of filter is designed specificallyto reflect IR and transmit the visible light. Filters on the lightsource can be made according to the below described procedures. Multiplelayers of films can be added to get the correct optical density ofabsorbing materials.

Exemplary methods of producing an absorbing film are disclosed below.Parameters, such as the quantities of chemicals, amounts of time, andtemperatures used as well as the selection of chemicals and variousprocedures performed can all be altered without deviating from thespirit of the present invention.

To prepare a polymer film with IR and UV absorbing dyes, thin films ofpolystyrene and PMMA can be made that are optically clear. IR absorbingdyes can be incorporated into these films. It has been found that aconcentration of approximately 0.54% total dye in polymer can work wellfor the purposes of the present invention. UV absorbing dyes can beincorporated in the PS-IR films as well.

An example method of making a PMMA film of the present invention isdescribed below. PMMA films of varying thickness with a constantconcentration 20.008 g of PMMA (Mw=350,000 Aldrich) are dissolved inapproximately 100 mL of dichloromethane. To this solution 0.025 g Epolin4105, 0.026 g Epolin 4138, 0.029 g Epolin 3130, and 0.025 g Epolin 1125are added after being dissolved in dichloromethane. Next aliquots of4.5, 9.0, 13.5, and 18.0 mL of the polymer/dye solution are removed andplaced in aluminum trays to dry. In order to slow the drying process,trays of the resulting material can be covered with small funnels. Afterdrying, the thickness of the films can be determined using a modifiedMitutoyo Absolute ID-S 1012 instrument. The effectiveness of the filmscan also be determined by using NVGs with an attached 890 nm shortpassfilter. Results of such are located in the table below.

Volume Added Sample (mL) Film Thickness (mm) Effectiveness Rating 26-A24.5 0.27 4 26-B2 9.0 0.4 3 26-C2 13.5 0.63 2 26-D2 19.0 0.66 1

The final average dye concentration might be 1.3 mg dye/g polymer or5.25 mg/total dye/g polymer. An increase in film thickness can improvethe effectiveness of the film as an infrared wavelength blocker.

A second example method of preparing a polymer film with IR and UVabsorbing dyes is described below. The chemicals used and describedbelow are abbreviated as follows; Polystyrene (PS), Poly methylmethacrylate (PMMA), Glaze Coat Epoxy (Part A and Part B), EnvirotexLite Pour-on High Gloss Finish, Epolin 1125, Epolin 1175, Epolin 4105,Epolin 4138, Epolin 4139, Tinuvin 292, Tinuvin 328, Tinuvin 770 DF,Tinuvin 5060, Lowite 5060, and Dichloromethane.

The polymer films are made with various concentrations of absorbing dyesas follows. 2.5 g of PMMA is dissolved in CH₂Cl₂. A solution of 0.5%absorbing dye (Epolin 4105) and 0.5% 4138 in CH₂Cl₂ is prepared and therequired amount is added to make concentrations of 0.05, 0.01, 0.005,and 0.001% of each dye. The resulting solution is then mixed. Two filmsare then prepared. One film is a thin film and the other film is athicker film. The films are allowed to dry in air in an aluminum dish.The optical clarity of the films can then be observed after drying. Thefilms formed are optically clear.

In addition to preparing thin films containing absorbing dye (Epolin4105), thin films may be prepared with various concentrations of Epolinabsorbing dyes 4138 and 4139 as follows. 5.0 g of PMMA is dissolved inapproximately 30 mL of CH₂Cl₂. A solution of 0.5% 4138 and 0.5% 4139 inCH₂Cl₂ is prepared and the required amount is added to makeconcentrations of 0.05 and 0.01% of each dye. Two films of differentthicknesses are then prepared, one thin and the other thick, and allowedto dry in air. Each resulting thin film is substantially opticallyclear.

Another example of polystyrene films is prepared after placing them in avacuum chamber. These films are prepared as follows. 5.0 g of PS isdissolved in approximately 30 mL of CH₂Cl₂. Next a solution of 0.5%Epolin 4105 and 0.5% Epolin 4138 is added and mixed. Part of thesolution is placed into an aluminum dish and then placed in the vacuumchamber to remove the solvent. The optical clarity of the resultingfilms is substantially free of bubbles and is optically clear. Otherfilms might contain some bubbles but can still be optically clear.

Infrared absorbing dyes can be made in different epoxies as follows.Equal parts of epoxy are placed in a centrifuge along with variousamounts of 0.5% Epolin 4105 and 0.5% Epolin 4138 dye solution inchloroform. This is mixed for approximately 3 minutes and then placed inmetal or plastic containers. These samples are then placed in the vacuumchamber with no heat until no bubbles are observed. The heat can beraised to approximately 120° C. for approximately one hour. The samplescan be removed and the film can be observed. If heat is applied beforeall the chloroform is removed, bubbles might be present in the finalfilm. However, in the event that the chloroform is removed under vacuum,bubbles should not be present in the final film and the films should besubstantially optically clear.

An example of infra-red absorbing dyes in optically clear glaze coatepoxy can be prepared as follows. 2 mL of Part A and 2 mL of Part B ofthe above mentioned Glaze Coat epoxy is mixed for approximately 3minutes. Epolin dye solution is added so that 0.25, 0.5, 0.75, and 1.0mL of dye at 0.5% 4105 and 0.5% 4138 solution is present. The mixture ismixed and then added to various molds. The different molds can theneither be placed in an oven or placed under a vacuum to produce films.

A thin film of polystyrene with a concentration of 1% Epolin 4105 and 1%Epolin 4138 can then be prepared as follows. 10.0 g of PS is dissolvedin approximately 60 mL of CH₂Cl₂. 0.9 g increments of the dye solutionare then be added (for example, 5 additions total). After each addition,approximately 3 mL of the solution is removed and placed into analuminum dish. This dish is then covered with a styrofoam cup with thebottom removed to dry. The resulting films are substantially opticallyclear. FIG. 2 shows the UV-Visible spectrum of the film prepared afterthe 3^(rd) addition, 2.7 g of solution is added. As can be readily seenin FIG. 2, this film can strongly absorb wavelengths between 800 nm and1000 nm.

Two polystyrene films can be prepared such that they may be placed on oraround the headlight of a vehicle. These polystyrene films can beprepared using 3.6 g of Epolin 4105 and 4138 dye solution. Two 10.0 gsamples of PS dissolved in CH₂Cl₂ can be prepared. Next, 3.6 g of the 1%4105 and 1% 4138 dye solution can be added and then mixed. Thesesolutions can then be added to two aluminum containers of differentsizes in a desired form. The containers can be placed under funnels andallowed to dry. The resulting solution can both absorb the desiredwavelengths of light and be optically clear.

Two polystyrene films containing Epolin 1125 and Epolin 1175 dye can beprepared as follows. Two 10.0 g samples of PS dissolved in CH₂Cl₂ areprepared. Next, 2.7 g of either 1% Epolin 1125 or 1% Epolin 1175 dyesolution is added. Then, approximately 3 mL of the solution is placed inan aluminum dish and allowed to dry under a styrofoam cup funnel. Bothsolutions form optically clear films. The resulting UV-Vis Spectra ofeach film are shown in FIG. 3. As can be seen in FIGS. 4 and 5, the IRabsorbance of the Epolin 1125 and Epolin 1175 is not as great as withthe Epolin 4105 and Epolin 4138.

Two polystyrene films of Epolin 4105 and Epolin 4138 can be preparedwith UV absorbers to prevent degradation as follows. A 5% solution ofeach UV blocker can be prepared in CH₂Cl₂. Next, a 1:100 dilution can bemade and the UV-Vis spectrum obtained. The spectrums of these films arerepresented in FIG. 4 and compared to that of Epolin 1125 and 1175above. Next four thin films can be cast using Tinuvin 292, 770 DF, 5060,and Lowite 234 PW at 4.0 g of the 5% solution. The UV-Vis can be takenfor these resulting films (see FIG. 5). The UV-Vis of the 2.7 g solutionis also present for comparison of the UV absorbance. The UV absorbers234 PW and 5060 can absorb much of the UV from 200-400 nm while theabsorbers 292 and 770 DF only absorb a narrow range around 250 nm. Theaddition of the first three absorbers to the film can increase theabsorbance around the 400 nm portion without increasing the totalabsorbance in the UV region.

With respect to the thin films of polystyrene it is apparent that thesefilms can be made that are optically clear. Additionally, IR absorbingdyes can be incorporated into these films and UV absorbing dyes can beincorporated in the PS-IR films.

Another example of a filter for the light source can be prepared bybuilding a multilayer structure UV hot mirror comprising two hot mirrorsand an interference film. As illustrated in FIG. 6, this multilayer filmcan be very effective blocking the NIR light from the illuminationsource as well as allowing a near colorless visible light through asshown in the Visible-Near IR spectrum of the multilayer film. Similarfilters can be built using mirrors from Navistar, and many other hotmirrors can be used in this type of filter.

In a system embodying aspects of the present invention, headlights of anautomobile such as an ambulance, police car, or fire truck might beconfigured with NIR absorbing filters such that substantially onlyvisible light is emitted while the near IR component is removed.Materials that substantially absorb infrared light while allowing forvisible light to pass can include YAG laser filters and absorbing dyes.A headlight treated with these absorbing dyes might appear the same tothe naked eye as an untreated headlight, but the treated headlight willnot emit infrared light. Thus, with the use of an image receiverconfigured to detect infrared light, a user of the system can identifyautomobiles that are not ambulances, police cars, or fire trucks.

The foregoing description and examples have been set forth merely toillustrate the invention and are not intended as being limiting. Each ofthe disclosed aspects and embodiments of the present invention may beconsidered individually or in combination with other aspects,embodiments, and variations of the invention. In addition, unlessotherwise specified, none of the steps of the methods of the presentinvention are confined to any particular order of performance.Modifications of the disclosed embodiments incorporating the spirit andsubstance of the invention may occur to persons skilled in the art andsuch modifications are within the scope of the present invention.Furthermore, all references cited herein are incorporated by referencein their entirety.

1. A system comprising: a first light source configured to emit light ata first set of wavelength bands; a transmitting filter to blocktransmission of a first subset of the first set of wavelength bands; areceiving filter configured to block transmission of a second subset ofthe first set of wavelength bands, wherein the first and second subsetsare not identical; and an image receiver configured to discriminatebetween the first light source and other light sources by engaging thereceiving filter.
 2. The system of claim 1, wherein the receiving filteris configured to allow transmission of a wavelength band included in thefirst subset but not in the second subset.
 3. The system of claim 1,wherein the transmitting filter is configured to transmit only visiblelight.
 4. The system of claim 1, wherein the image receiver isconfigured to detect light in the non-visible spectrum.
 5. The system ofclaim 1, wherein the transmitting filter blocks infrared wavelengths andthe receiving filter allows for the transmission of infraredwavelengths.
 6. The system of claim 1, wherein the first light sourceand transmitting filter are coupled to an automobile.
 7. The system ofclaim 1, wherein the transmitting filter is a surface treated with amaterial having a specific absorption spectrum.
 8. The system of claim1, wherein the transmitting filter is an interference filter.
 9. Thesystem of claim 1, wherein the transmitting filter is a hot mirror. 10.The system of claim 1, wherein the transmitting filter is an injectedmolded part containing absorbing dyes.
 11. The system of claim 1,wherein the image receiver is a camera connected to a display monitor.12. The system of claim 1, wherein the receiving filter may bemechanically or electrically engaged by the image receiver.
 13. A systemcomprising: a first light source configured to emit light in theinfrared spectrum; a transmitting filter to block transmission of a setof wavelength bands within the infrared spectrum; and an image receiverconfigured to identify the set of wavelength bands.
 14. The system ofclaim 13, wherein the first light source and transmitting filter arecoupled to an automobile.
 15. The system of claim 13, wherein thetransmitting filter is a surface treated with a material having aspecific absorption spectrum.
 16. The system of claim 13, wherein thetransmitting filter is an injected molded part containing absorbingdyes.
 17. The system of claim 13 wherein the image receiver is a cameraconnected to a display monitor.
 18. A system comprising: a first lightsource; a transmitting filter to block transmission of wavelength bandswithin the infrared spectrum; and an image receiver configured to detectwavelength bands in the infrared spectrum, the image receiver configuredto distinguish between a second light source emitting light in theinfrared spectrum and the first light source.
 19. The system of claim18, wherein the first light source and transmitting filter are coupledto an automobile.
 20. The system of claim 18, wherein the transmittingfilter is a surface treated with a material having a specific absorptionspectrum.
 21. The system of claim 18, wherein the transmitting filter isan injected molded part containing absorbing dyes.
 22. The system ofclaim 18 wherein the image receiver is a camera connected to a displaymonitor.